1. Field of the Invention
The present invention relates to an improved method for injecting a molten metal into the cavity of a mold of a vertical diecasting machine.
2. Description of Relevant Art
Generally, known diecasting methods have various attendant problems in that the air or gases existing in the mold cavity obstruct or resist the flow of the molten metal into all parts of the mold cavity, and the air or gases are likely to be trapped in the casting, forming undesirable cavities and thus degrading the precision and quality of the casting.
In conventional diecasting, to evacuate the air or gases existing in the mold cavity, various methods have been proposed. For example, U.S. Pat. No. 3,209,416 discloses a method wherein a labyrinth passage is formed at the pouring basin through which the air or gases are sucked out by a vacuum device, while in Japanese Patent Publication No. 13206/79 the pouring basin communicates with the circumference of the mold by means of an air vent. The former method is disadvantageous in that it requires a vacuum device and other additional apparatus. Further, complex procedures are required in controlling the casting conditions, handling of the molds and controlling the molten metals, and the cost of the castings is thus adversely affected. The latter method is also disadvantageous, in that evacuation of the air or gases existing in the mold cavity is insufficient since the pressure in the mold cavity increases rapidly when the molten metal is injected into the mold cavity and production of castings of high quality similar to those produced by gravity diecasting (GDC) is difficult since the back pressure which works on the molten metal flowing in the mold cavity causes unbalanced flow of the molten metal, thus promoting the inclusion or trapping of air or gases in the castings.
The present invention provides an improved method of diecasting which eliminates the foregoing disadvantages attendant the above-described conventional methods.